Why do lots of programmers move commas to the next line? [closed]

Answer 1

I think it's done so that it's easier to spot a missed comma.

var something = 0,
    foo = "a string",
    somethingElse = []
    bar;

var something = 0
  , foo = "a string"
    somethingElse = []
  , bar;

Answer 2

This is because the comma belong to the new line next statement and not the previous one. (As @Dave Newton states it in his comment below: the pseudo-BNF would be foo [, foo]*-ish)

For example:

If you have this:

a,
b,
c

If you need to remove the c then you need to delete two things: de c and the comma on the previous line. If you do this:

a
,b
,c

now you only need to delete the ,c line. It makes more sense this way, because the comma behind the b in the first example only is needed because of the c. It does look worse this way though. It's a trade off between maintainability of your code and the way it looks.

Answer 3

You might be looking at generated code, for instance, when writing a loop to generate an SQL select statement sometimes I will write it like:

sql =  "SELECT";
sql += "  table.id"; // or some field that will always be in the query
for (var i = 0; i < 10; i++;) {
  sql += ",  table.field" + i; 
}
sql += "FROM table" // etc

Instead of adding the comma at the end and then having a condition to omit it on the last iteration of the loop or doing:

sql =  "SELECT";
for (var i = 0; i < 10; i++;) {
  sql += "  table.field" + i + ","; 
}
sql += "  table.id";
sql += "FROM table" // etc

Which is functionally equivalent, but then the ID doesn't appear where I usually want it.